Sprout is one of the companies that came out of stealth at DEMO recently and they have now introduced their public beta. Check out their site and you’ll see all sorts of cool examples of the kinds of widgets (or Sprouts) that folks are building. What’s especially cool to me is that the Builder is built in Flex and the Sprouts also are Flex-based (though I’m not sure how much of the framework the Sprouts themselves use).
And with Flex 3 being free and open source, Sprout is able to build this kind of hosted service that generates tons of Flex apps for free (though I think they chose to buy a few Flex Builder licenses to make it easier). Pretty sweet!